Flywheel on a rotary phase convertor
Christopher Tidy
I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor. I've heard varying opinions on the subject.
Having thought about it myself, I've reached the following conclusions:
(i) The sag in voltage on the third line is caused by the fact that it
is not connected directly to the supply. The flywheel doesn't change
this. Nor will it change the steady speed at which the rotor turns, so
unless it has some averaging effect on a cycle-by-cycle basis which I
haven't considered, it won't affect the quality of the three phase
output when the convertor is running in a steady state.
(ii) It might be an advantage when trying to plug reverse the load
motor. As far as I can see (on the most simplistic level), the motor
with the most kinetic energy will win.
I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get
a flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.
Any opinions and arguments? Thoughts would be appreciated...
Best wishes,
Chris
jim rozen
>
>Hi all,
>
>I'm trying to figure out if there is any benefit in adding a flywheel to
>a rotary phase convertor.
There is no experimental data on this subject as far as I can see.
I have seen coherent, cogent arguments from respected folks
that support both views - one that it will help, the other that it
will hinder.
Those who suggest a flywheel is bad say that rotary converters
deliver transient power to the generated phase by allowing the rotor to
slip, and a flywheel prevents this.
Those who suggest a flywheel is good say that that flywheels store
rotational energy and will this is made available to transient loads.
Those two preceeding statements are pure paraphrase on my part, and
I of course apologize if I have mis-represented anyones comments.
But there's no empirical data out there as far as I can tell.
It wouldn't be that hard to instrument and measure.
Jim
--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================
Grant Erwin
to see considerable evidence of arcing near the contacts in the drum switch. I
figured that plug reversing it was the reason - a LOT of current flows, and
motors with all their inductance do NOT like current changes. So regardless of
what you do with your phase convertor, I strongly suggest that you not plug
reverse anything using a drum switch unless that switch is extremely heavily built.
I know of no value in adding rotary mass. The armature of an idler motor is
already quite a bit of rotary mass.
GWE
Jim Wilson
> I'm trying to figure out if there is any benefit in adding a flywheel to
> a rotary phase convertor.
A flywheel would reduce, not increase, the idler's ability to respond to
load changes. When the electrical load on the idler increases, the
idler's rate of rotation falls (I.e., the slip increases). This raises
the current draw from the single phase source. The higher winding current
increases the strength of the rotating magnetic field in the idler, which
pushes the generated third leg voltage up. The upshot of all this is that
the response rate of the third leg voltage to electrical load changes is
inversely related to the inertia of the idler's armature.
That's my understanding. Perhaps one of the old regulars can explain it
better. Is Fitch still around? I seem to remember his doing some tests on
this very thing a few years back.
Jim
Rex B
jim rozen wrote:
> In article <43BAE770...@cantabgold.net>, Christopher Tidy says...
>
>>Hi all,
>>
>>I'm trying to figure out if there is any benefit in adding a flywheel to
>>a rotary phase convertor.
>
>
> There is no experimental data on this subject as far as I can see.
>
> I have seen coherent, cogent arguments from respected folks
> that support both views - one that it will help, the other that it
> will hinder.
>
> Those who suggest a flywheel is bad say that rotary converters
> deliver transient power to the generated phase by allowing the rotor to
> slip, and a flywheel prevents this.
>
> Those who suggest a flywheel is good say that that flywheels store
> rotational energy and will this is made available to transient loads.
Then maybe one needs a "dual-mass" flywheel like they are putting on the
diesel pickups now.
Don Foreman
<ignoram...@NOSPAM.29795.invalid> wrote:
>> (ii) It might be an advantage when trying to plug reverse the load
>> motor. As far as I can see (on the most simplistic level), the motor
>> with the most kinetic energy will win.
>
>I am not sure why you think so. Would you clarify why you think that
>plug reversing a load motor would somehow slow down the idler
>motor. The idler, after all, spins with the frequency of the AC
>mains.
>
No it doesn't. It rotates at less than synchronous speed. If it ran
at synch speed there would be no slip hence no induction in the
rotor.
Christopher Tidy
Thanks for all the responses.
> A flywheel would reduce, not increase, the idler's ability to respond to
> load changes. When the electrical load on the idler increases, the
> idler's rate of rotation falls (I.e., the slip increases). This raises
> the current draw from the single phase source. The higher winding current
> increases the strength of the rotating magnetic field in the idler, which
> pushes the generated third leg voltage up. The upshot of all this is that
> the response rate of the third leg voltage to electrical load changes is
> inversely related to the inertia of the idler's armature.
I'm not sure about this. Yes, it will take longer for the rotor's speed
to fall, but surely the stored energy will be dissipated by driving
extra current through the load?
Best wishes,
Chris
Robert Swinney
It isn't. Think more of the RPC as a network in which parts of it rotate in
order to supply current throughout. Part of the RPC is the load motor. The
idler generates nothing without the load as part of a network. IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can be
viewed as series resonant circuits. Such circuits are "tuned" via
capacitance placed in series.
Bob Swinney
"Jim Wilson" <jwi...@paragoncode.com> wrote in message
news:MPG.1e24aaf25...@newsgroups.comcast.net...
Don Foreman
wrote:
>In article <43BAE770...@cantabgold.net>, Christopher Tidy says...
>>
>>Hi all,
>>
>>I'm trying to figure out if there is any benefit in adding a flywheel to
>>a rotary phase convertor.
>
>There is no experimental data on this subject as far as I can see.
>
>I have seen coherent, cogent arguments from respected folks
>that support both views - one that it will help, the other that it
>will hinder.
>
>Those who suggest a flywheel is bad say that rotary converters
>deliver transient power to the generated phase by allowing the rotor to
>slip, and a flywheel prevents this.
>
>Those who suggest a flywheel is good say that that flywheels store
>rotational energy and will this is made available to transient loads.
>
>Those two preceeding statements are pure paraphrase on my part, and
>I of course apologize if I have mis-represented anyones comments.
>But there's no empirical data out there as far as I can tell.
>
>It wouldn't be that hard to instrument and measure.
>
>Jim
Some kinetic energy is necessary for the thing to work, but my bet is
that the rotor has more than enough and more would not help.
Kinetic energy is necessary for the idler to produce power in the
third leg during parts of the cycle when less or none is being drawn
from the mains. Energy is also stored in the magnetic field, but its
ebb and flow is in quadrature with third leg power. This is a
cycle-by-cycle event: it accelerates (accumulates energy) during
part of each cycle and decelerates (gives up energy) during other
parts of each cycle. The result is speed ripple, which would be
greater for rotors with small moments of inertia.
The power levels drawn and delivered are a function of slip speed
which governs both stator current and induced emf -- back emf in the
case of the driven windings and generated emf in the case of the third
leg. As the third leg produces more countertorque from higher
current flow thru it, the rotor will slow until slipspeed has
increased to the point where enough power is drawn from the mains to
regain equilibrium.
Observers (Jerry and Fitch) have said they didn't note much change in
idler slipspeed with varying loads. However, resolution of 1% or
better would be necessary to see speed variations because the slip
speed range from no load to full load in most induction motors is
only a few percent at most.
Don Foreman
Yes, but power is the rate of energy flow. The amount of power it
can produce for the third leg (energy delivered per cycle) is a
function of slip speed, and field strength hence stator current which
is also a function of slip speed.
jim rozen
>
>IMO, you need to lose the thinking of a RPC as being a form of generator.
>It isn't. Think more of the RPC as a network in which parts of it rotate in
>order to supply current throughout. Part of the RPC is the load motor. The
>idler generates nothing without the load as part of a network. IMO, a
>flywheel on the idler cannot act as anything more than additional dynamic
>load on the network. It would be aprox. the same to put the flywheel on the
>load motor instead. Forget flywheels and spend the money on enhancing the
>idler-load network with proper capacitance. Complex current flows in all
>parts of the RPC. In simplistic terms, the idler-load current paths can be
>viewed as series resonant circuits. Such circuits are "tuned" via
>capacitance placed in series.
Granted this kind of tuning is the very *first* thing one would do
before considering flywheels.
I specifically recall Gary Coffman claiming they would reduce transient
response, and yet there's a considerable group of well-informed
individuals on the practical machinist board who say they improve
matters.
I have to say I find *both* sides to be persuasive, at least at the
'hand-waving' level.
My suspicion is that flywheels probably help up to a point, if one
models the rotor as having zero mass to start with. And that the
optimum flywheel size will wind up being about one rotor unit in
size! This is what a former boss of mine calls 'the schwarz law
of the initial maximum.'
Ie, if it works the first time you set it up, anything you do to it
after that makes it work worse.
:^)
Jim Wilson
> IMO, you need to lose the thinking of a RPC as being a form of generator.
Hrm. Is this in response to my post, or Christopher's? I don't think I
view a RPC as a generator at all. Perhaps it's more like a rotating
transformer.
<snip>
> It would be aprox. the same to put the flywheel on the
> load motor instead.
Most of what you said seemed reasonable (I snipped all the
unobjectionable parts), but this statement can only be true under limited
conditions. There would be a large difference in performance between the
two systems for example when plug reversing is used.
Cheers,
Jim
Robert Swinney
FWIW, you might view a plug reverse of the load motor as the worst case
flywheel effect.
Bob Swinney
bam...@localnet.com
were spinning the rpc up by hand before cutting in the power to lessen
the duration of high current draw.
sn...@trippin.net
wrote:
>In article <UJSdnR0LaPQ...@comcast.com>, Robert Swinney says...
We just call that syndrome "fix it 'til it's broke".
Snarl
Wayne Cook
<cdt22...@cantabgold.net> wrote:
>I can't seem to find any used flywheels to fit my motor, but I can get a
>brand new flywheel for £40. I'm not sure if it is worth it in order to
>satisfy my scientific curiousity. If I get a different motor, I can get
>a flywheel for next to nothing, but that will involve lots of effort,
>bartering and deals in order to get a motor which isn't quite so cool.
>
I won't touch the theoretical discussions on this thread. However I
thought I might mention that if you wanted to experiment cheaply I'm
sure you can find a used cast iron pulley in large enough diameter to
serve as your flywheel. Preferably a multi-groove pulley.
Wayne Cook
Shamrock, TX
http://members.dslextreme.com/users/waynecook/index.htm
DoN. Nichols
> On Tue, 3 Jan 2006 21:07:42 +0000 (UTC), Christopher Tidy <cdt22...@cantabgold.net> wrote:
[ ... ]
> > (ii) It might be an advantage when trying to plug reverse the load
> > motor. As far as I can see (on the most simplistic level), the motor
> > with the most kinetic energy will win.
>
> I am not sure why you think so. Would you clarify why you think that
> plug reversing a load motor would somehow slow down the idler
> motor. The idler, after all, spins with the frequency of the AC
> mains.
I have read reports here of under-rated rotary converters
actually reversing, instead of the load motor, when plug reversing. I
think that the flywheel might indeed solve this problem.
Enjoy,
DoN.
--
Email: <dnic...@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Don Foreman
<jud...@comcast.net> wrote:
>IMO, you need to lose the thinking of a RPC as being a form of generator.
>It isn't. Think more of the RPC as a network in which parts of it rotate in
>order to supply current throughout. Part of the RPC is the load motor. The
>idler generates nothing without the load as part of a network.
Sure it does. With the idler spinning, a voltage is generated in
the third leg that is in quadrature to line voltage, even if there are
no capacitors anywhere. Transformer action can not produce a
quadrature voltage so it must be (and is) generated by the rotating
rotor field -- which always is in quadrature with the stator field.
> IMO, a
>flywheel on the idler cannot act as anything more than additional dynamic
>load on the network. It would be aprox. the same to put the flywheel on the
>load motor instead. Forget flywheels and spend the money on enhancing the
>idler-load network with proper capacitance. Complex current flows in all
>parts of the RPC. In simplistic terms, the idler-load current paths can be
>viewed as series resonant circuits.
If there are capacitors. But idlers without any run caps still work.
In fact, they work quite well if they're large enough.
Dave Gee
advantage of great kinetic energy with very understressed component
parts. I favor a pony to "spin up" the first started (should be
largest by 1.5) motor.
Don Young
wouldn't plug reversing with identical motors and no mechanical load have an
equal chance of reversing either motor? When running free, it seems to me
that either motor could be considered to be the source or load for the third
phase leg. I tend to believe that the idler requires more mechanical inertia
than the load to maintain the best functioning.
If an induction motor does not "generate", is induced counter EMF imaginary
and the use of common induction motors as generators impossible? There are
many ways to understand and describe how things work and I like to think of
the RPC as simply a running induction motor with the magnetized rotor
inducing EMF not only into the line energized windings (counter EMF) but
also into the unenergized and phase displaced windings. Note that, when
disconnected and still turning, an induction motor still has voltage across
its windings and loading this voltage with "braking" resistors will
mechanically load the rotor. I do not claim that this is the only way to
describe it or that any description can change the operating principles
involved.
Don Young
"Christopher Tidy" <cdt22...@cantabgold.net> wrote in message
news:43BAE770...@cantabgold.net...
Robert Swinney
"Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
news:bojmr1tum17kbp87a...@4ax.com...
> On Tue, 3 Jan 2006 17:20:12 -0600, "Robert Swinney"
> <jud...@comcast.net> wrote:
>
>>IMO, you need to lose the thinking of a RPC as being a form of generator.
>>It isn't. Think more of the RPC as a network in which parts of it rotate
>>in
>>order to supply current throughout. Part of the RPC is the load motor.
>>The
>>idler generates nothing without the load as part of a network.
>
> Sure it does. With the idler spinning, a voltage is generated in
> the third leg that is in quadrature to line voltage, even if there are
> no capacitors anywhere. Transformer action can not produce a
> quadrature voltage so it must be (and is) generated by the rotating
> rotor field -- which always is in quadrature with the stator field.
No load, no generation, Don. An idler running with no load motor does not
constitute a RPC. The network and supported current flow through that
network makes a RPC. Remember the idler is running as a single-phase
machine and the 3rd leg is open, that is, until it is connected into a RPC.
>> IMO, a
>>flywheel on the idler cannot act as anything more than additional dynamic
>>load on the network. It would be aprox. the same to put the flywheel on
>>the
>>load motor instead. Forget flywheels and spend the money on enhancing the
>>idler-load network with proper capacitance. Complex current flows in all
>>parts of the RPC. In simplistic terms, the idler-load current paths can
>>be
>>viewed as series resonant circuits.
>
> If there are capacitors. But idlers without any run caps still work.
> In fact, they work quite well if they're large enough.
OK. So they aren't series resonant circuits when there are no run caps -
granted. But the interconnection of idler and load and their associated
current paths are the same, even without run caps.
>
>
Robert Swinney
"Since the running idler and load motors are directly connected in parallel
. . ."
You are right about there being "many ways to understand and describe how
things work" but the concept of an idler and load motor's respective
windings being in parallel is not one of them.
Bob Swinney
"Don Young" <no...@nonesuch.com> wrote in message
news:11rmmd3...@corp.supernews.com...
B.B.
Rex B <r...@wmautomotive.com> wrote:
[...]
>Then maybe one needs a "dual-mass" flywheel like they are putting on the
>diesel pickups now.
That sounds like an interesting thingy. Got any details on it?
--
B.B. --I am not a goat! thegoat4 at airmail dot net
Gunner
wrote:
>Those who suggest a flywheel is bad say that rotary converters
>deliver transient power to the generated phase by allowing the rotor to
>slip, and a flywheel prevents this.
>
>Those who suggest a flywheel is good say that that flywheels store
>rotational energy and will this is made available to transient loads.
>
>Those two preceeding statements are pure paraphrase on my part, and
>I of course apologize if I have mis-represented anyones comments.
>But there's no empirical data out there as far as I can tell.
>
>It wouldn't be that hard to instrument and measure.
>
>Jim
Dont forget a nice heavy rotor IS a flywheel.
Gunner
The aim of untold millions is to be free to do exactly as they choose
and for someone else to pay when things go wrong.
In the past few decades, a peculiar and distinctive psychology
has emerged in England. Gone are the civility, sturdy independence,
and admirable stoicism that carried the English through the war years
. It has been replaced by a constant whine of excuses, complaints,
and special pleading. The collapse of the British character has been
as swift and complete as the collapse of British power.
Theodore Dalrymple,
jim rozen
>No load, no generation, Don. An idler running with no load motor does not
>constitute a RPC. The network and supported current flow through that
>network makes a RPC. Remember the idler is running as a single-phase
>machine and the 3rd leg is open, that is, until it is connected into a RPC.
No current flow, yes. But the third leg does come up in voltage, even
when open circuited. While it won't do any work, folks would be tempted
to say that the third leg is indeed "generated" even when it's open
circuited. Another one of those semantic mine fields....
Steve Smith
in parallel; swap a lead on either motor and the "bigger" one wins. I
still am not sure if a flywheel has any significant effect on which one
is bigger (though it seems like it would).
Steve
dca...@krl.org
Robert Swinney wrote:
> IMO, you need to lose the thinking of a RPC as being a form of generator.
>
In my opinion you need to realize that a RPC is an induction generator.
As far as flywheels are concerned, a flywheel will keep the slip angle
from changing as quickly. So a RPC without a flywheel will draw power
from the mains more quickly when the load is increased. Score points
for that side. On the other hand, a RPC with a flywheel will draw
power from the flywheel when the load is increased as well as from the
mains. So score points for the other side.
In the real world, it does not make much difference as the change in
speed of the RPC should be slight, and therefore only a small amount of
power can be drawn from the flywheel. Having a flywheel would help
with an undersized RPC when the load motor is plugged.
Dan
Robert Swinney
">> Sure it does. With the idler spinning, a voltage is generated in
>> the third leg that is in quadrature to line voltage, even if there are
>> no capacitors anywhere. Transformer action can not produce a
>> quadrature voltage so it must be (and is) generated by the rotating
>> rotor field -- which always is in quadrature with the stator field."
I'm not sure what you mean, Don. You said "Transformer action can not
produce a quadrature voltage so it must be (and is) generated by the
rotating rotor field -- which always is in quadrature with the stator
field".
Firstly, I don't understand why the issue must be complicated by bringing
the rotor field into the picture. It is well known the stator field and
rotor field are more or less locked into rotation at the same speed, but it
is incongruous to speculate the rotor field is solely responsible for the
stator field's third leg voltage. Remember we are essentially talking about
a single phase motor here with an open coil connected to the center point of
the line-fed main winding. I respectfully submit the third leg voltage is
not in quatrature with line voltage. The only way for that to be a true
statement would be in the special case of a precise amount of capacitance
connected from one line side to the end of the 3rd leg coil; an amount of
capacitance (start cap if you will) necessary to achieve an exact 90 degree
phase shift between line voltage and the 3rd. leg.
Bob Swinney
Don Foreman
<jud...@comcast.net> wrote:
>Don Young sez:
>
>"Since the running idler and load motors are directly connected in parallel
>. . ."
>
>You are right about there being "many ways to understand and describe how
>things work" but the concept of an idler and load motor's respective
>windings being in parallel is not one of them.
>
>Bob Swinney
Hey, Bob, what about delta-wound motors? Sure looks parallel to me!
Don Foreman
wrote:
>Since the running idler and load motors are directly connected in parallel,
>wouldn't plug reversing with identical motors and no mechanical load have an
>equal chance of reversing either motor? When running free, it seems to me
>that either motor could be considered to be the source or load for the third
>phase leg. I tend to believe that the idler requires more mechanical inertia
>than the load to maintain the best functioning.
Interesting! The relative impedances are also important here. The
larger motor with lower impedance (and probably higher inertia) will
govern. Look at the terminal voltage where the two third legs are
connected. If the motors were perfectly matched, their effects would
cancel and this terminal voltage would be zero. If they are not
matched, the voltage (phase) of that terminal will be determined by
the motor with the lower impedance, and the phase of this voltage
determines (or indicates) the direction in which both motors turn.
>
>If an induction motor does not "generate", is induced counter EMF imaginary
>and the use of common induction motors as generators impossible? There are
>many ways to understand and describe how things work and I like to think of
>the RPC as simply a running induction motor with the magnetized rotor
>inducing EMF not only into the line energized windings (counter EMF) but
>also into the unenergized and phase displaced windings.
Right, up to here.
> Note that, when
>disconnected and still turning, an induction motor still has voltage across
>its windings and loading this voltage with "braking" resistors will
>mechanically load the rotor.
Only if the rotor has some significant permanent magnetism -- not
usually the case.
Robert Swinney
"Iggy style".
Do this: Visualize 2 deltas connected in "parallel" if you will..
Obviously the current paths through the branches, where the lines are
connected, are in parallel. Now look at the common point where the other 2
legs of both deltas connect together. Those points are no more in parallel
than they would be if they were between two wyes.
It may be helpful to look at the configuration in its wye equivalent. Same
thing. All this speaks to the very complex current flow in an idler and
load connected as a RPC. Two 3-phase induction motors running on the same
3-phase line do not constitute a RPC. A RPC is two 3-phase induction motors
running on single-phase current. Capacitor augmentation assists in tuning
the network such that it appears to be operating from a 3-phase line.
Bob Swinney
"Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
news:u8unr1ddglc57h6ao...@4ax.com...
Robert Swinney
See my previous post, where I tried to show 2 induction motors operating
from single phase current in a RPC configuration cannot be in parallel.
Bob Swinney
"Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
news:8mvnr19csttj5i7tf...@4ax.com...
Don Foreman
<jud...@comcast.net> wrote:
>Don sez:
>">> Sure it does. With the idler spinning, a voltage is generated in
>>> the third leg that is in quadrature to line voltage, even if there are
>>> no capacitors anywhere. Transformer action can not produce a
>>> quadrature voltage so it must be (and is) generated by the rotating
>>> rotor field -- which always is in quadrature with the stator field."
>
>I'm not sure what you mean, Don. You said "Transformer action can not
>produce a quadrature voltage so it must be (and is) generated by the
>rotating rotor field -- which always is in quadrature with the stator
>field".
>
>Firstly, I don't understand why the issue must be complicated by bringing
>the rotor field into the picture.
Because it's there, producing phase shifts and emf's that cannot be
produced by a network of similar topology having only R's and L's.
> It is well known the stator field and
>rotor field are more or less locked into rotation at the same speed, but it
>is incongruous to speculate the rotor field is solely responsible for the
>stator field's third leg voltage. Remember we are essentially talking about
>a single phase motor here with an open coil connected to the center point of
>the line-fed main winding. I respectfully submit the third leg voltage is
>not in quatrature with line voltage. The only way for that to be a true
>statement would be in the special case of a precise amount of capacitance
>connected from one line side to the end of the 3rd leg coil; an amount of
>capacitance (start cap if you will) necessary to achieve an exact 90 degree
>phase shift between line voltage and the 3rd. leg.
The rotor field is always in space quadrature from the stator field.
This is well-established in about any textbook on the subject. That
being the case, the emf it induces in the third leg is necessarily
in quadrature with the emf impressed by the line (and countered by the
stator field) in the other two windings.
Now consider a Y-connected motor. Rotate the Y 30 degrees clockwise so
the right hand leg is horizontal, with line connected across the
lefthand legs. Note that the vertical components of the excited coil
windings add while the horizontal components cancel. Therefore,
there is no emf induced in the horizontal third winding by direct
transformer action. Emf induced in the third winding is therefore
solely due to the rotor field -- and since that field is in quadrature
with the stator field, the emf in the third winding must be in
quadrature with the excitation voltage. QED.
The terminal voltage on a loaded third winding will vary from exact
quadrature due to I Z drops, which have opposite sense in the excited
windings from those in a loaded third leg -- look at the directions of
current flow. . But if you connect a scope from third terminal to
neutral (center of the Y) in an unloaded idler, it would show an emf
in quadrature with line voltage.
Credit to Jerry Martes for showing me this aspect of induction idlers.
jim rozen
>The rotor field is always in space quadrature from the stator field.
>This is well-established in about any textbook on the subject. That
>being the case, the emf it induces in the third leg is necessarily
>in quadrature with the emf impressed by the line (and countered by the
>stator field) in the other two windings.
I thought it was the rotor *current* that was in quadrature.
Basically the rotor currents cause a rotating B field to
exist inside the stator. How it does this doesn't matter
much, but suffice it to say that the phase of the rotating
B field agrees with the incoming excitation (which of course
supplies all the power to the gizmo) which means it will
cause the correct phase voltage to exist on the third lead.
Don Foreman
<jud...@comcast.net> wrote:
>Hey, Don, it sounds like you are beginning to go off half cocked, sort of
>"Iggy style".
>
Look at
http://users.goldengate.net/~dforeman/delta_3D/
Colored lines are windings, white lines are connections.
'Splain to me how the windings of same colors are not in parallel...
Don "Half-cocked" Foreman
Don Foreman
<jud...@comcast.net> wrote:
>Don,
>
>See my previous post, where I tried to show 2 induction motors operating
>from single phase current in a RPC configuration cannot be in parallel.
>
I saw it. I just don't agree with it. See recent post showing things
in 3D.
Transform to Y using the usual Y-delta transforms if you like. See
any textbook on the subject.
In the Y case they don't look in parallel if there is no neutral
connection. However, since a delta depiction clearly shows that they
*ARE* in parallel, they are in freakin' parallel, BOB! Must I glue
up some popsicle sticks for you?
Can you explain the discrepancy? :<)
Hint: if there is no potential between unconnected points (the
neutrals in a Y configuration) then they are effectively connected.
Don "half-cocked" Foreman
half cocked my arse....grumble mutter ....chuckle
Robert Swinney
you were thinking of RPC's as well. Two 3-phase induction motors connected
as a RPC are not, repeat are not in parallel. I'm afraid you have jumped to
the conclusion that two 3-phase induction motors connected in RPC fashion
are merely connected in parallel. That is not the case. See a later post
in which I tried to explain the defference.
Bob (if it sounds like Iggy, it might be Iggy, No! it can't be) Swinney
"Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
news:om4or1h30ou6d9juk...@4ax.com...
Robert Swinney
colorful, drawings were not of a RPC configuration. Draw out a RPC and I
think you may understand. Oh! be sure to include some capacitors. They (in
electronic terms) might be considered as steering capacitors, for it is
their job to force the convoluted currents to flow in such a way as to
*emulate* true 3-phase. Note, I said *emulate* because current flow in a
RPC is not the same as current flow in parallel connected 3-phase motors, no
matter which transform is used.
Bob Swinney
"Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
news:mr4or15vae0bt47e3...@4ax.com...
Don Foreman
<jud...@comcast.net> wrote:
>Sorry, Don. We were discussing RPC's and I assumed (we know what that does)
>you were thinking of RPC's as well. Two 3-phase induction motors connected
>as a RPC are not, repeat are not in parallel. I'm afraid you have jumped to
>the conclusion that two 3-phase induction motors connected in RPC fashion
>are merely connected in parallel. That is not the case.
Mine is! Works fine.
Don Foreman
<jud...@comcast.net> wrote:
>Sorry, Don. We were discussing RPC's and I assumed (we know what that does)
>you were thinking of RPC's as well. Two 3-phase induction motors connected
>as a RPC are not, repeat are not in parallel. I'm afraid you have jumped to
>the conclusion that two 3-phase induction motors connected in RPC fashion
>are merely connected in parallel. That is not the case.
Hanrahan seems to think it is the case. The presence of the
capacitors notwithstanding, his motors are connected in parallel.
Don Foreman
<jud...@comcast.net> wrote:
>Well, Don - you've missed the point again! What part of "2 induction
>motors operating from single phase current in a RPC configuration cannot be
>in parallel" did you fail to understand.
The part that disagrees with an acknowledged authority, Mr. Hanrahan:
http://www.metalwebnews.com/howto/ph-conv/fig1.html
>Your well intentioned, and
>colorful, drawings were not of a RPC configuration. Draw out a RPC and I
>think you may understand.
I did. So did Hanrahan. His are in parallel.
http://www.metalwebnews.com/howto/ph-conv/fig1.html
> Oh! be sure to include some capacitors.
He did.
>They (in
>electronic terms) might be considered as steering capacitors, for it is
>their job to force the convoluted currents to flow in such a way as to
>*emulate* true 3-phase. Note, I said *emulate* because current flow in a
>RPC is not the same as current flow in parallel connected 3-phase motors, no
>matter which transform is used.
Convoluted currents? Yeesh! RPC's aren't witchcraft and wizardry,
mesh currents are mesh currents. The (parallel) caps provide some
phase correction and resonant voltage boost to compensate for the
reversal in I-Z drop because the third leg of the idler is a driving
leg rather than a driven leg. They are not essential to the
operation of an RPC, though they can improve balance.
My RPC has no capacitors, starts and plug-reverses my lathe and mill
just fine.
jim rozen
>
>Well, Don - you've missed the point again! What part of "2 induction
>motors operating from single phase current in a RPC configuration cannot be
>in parallel" did you fail to understand.
Probably the same one I can't see.
They look like they're in parallel to me. Unless I'm missing
something.
Granted the term "parallel" is a bit of a misnomer here but
each winding of my load motor is in fact in parallel with
a winding in the idler motor.
Jim (half cocked also?)
Robert Swinney
motor". The flawed logic is that a phase converter does not "run" a load
motor. Such a differentiation between phase converter and load motor is not
possible. An idler motor and load motor, taken together as a network, are
what constitutes a rotary phase converter. This all harks back to the
misunderstood "generator" concept as applied to an idler motor. The two
must work together to form a rotary phase converter. Remember a RPC (the
whole RPC) acts to manipulate current flow in a network so that the load
motor voltages, and currents, are the same as if the load motor was
operating from a 3-phase source. Remembering, all the while, the whole thing
is running on *single-phase* current.
Now as for parallel connectivity: The drawing is that of a classic RPC
(idler and load motor) operating from Hot 1 and Hot 2, both sides of a
single-phase source. Consider Hot 1. It connects to L1 of the idler motor
and also to L1 of the load motor. The same can be said for Hot 2 and the 2
respective L2's. By definition, the points designated as L1 and L2 in both
idler and load are operated in parallel across the line. That is to say the
2 main windings, L1 to L2 in your drawing of both idler and load are
connected in parallel across the line.
Now look at the way current flows in the L3 lead. The idler's L3 wire has 1
end connected to the 3rd. winding on the idler, call that a source point for
L3 current flow. The other end of wire L3 connects not to the analogous
same start point on the load motor but to a point on the other end of the
load motor's L3. This is not, can not, be considered a parallel connection.
The only way the two 3-phase motors could be connected in parallel is if
they are both fed from a 3-phase source.
In a manner of speaking, for a RPC (network) to do its thing, when taking in
*single-phase* current and delivering *3-phase current* to a load motor
(also part of the network) there has to be current flow in 2 directions the
3rd leg. Of course, aggregate current flow is such that current will flow
in the "right" direction in the load motor's 3rd leg. Parts of the RPC act
as both generators and consumers, thus the heavier element will cause
current to flow, seemingly backwards, into the other element. And so it is
with the RPC - capacitor augmentation can enhance the convoluted current
flow in such a way as to make emulated 3-phase current flow in the load
motor.
Bob Swinney
"Ignoramus18299" <ignoram...@NOSPAM.18299.invalid> wrote in message
news:BDVuf.25892$f26....@fe75.usenetserver.com...
> Here's how my phase converter is wired when it runs a load motor:
>
>
> idler Load
>
> L3-------------------------L3
> / \ / \
> L1 --- L2 L1---L2
> | | | |
> | +--------------------->---+
> +-----------------------------+ Hot2
> Hot1
>
> L1 connected to L1, L2 connected to L2, L3 connected to L3. L1 and L2
> are also connected to utility power Hot1 and Hot2.
>
> How are these motors not running in parallel?
>
> They are.
>
> Leg numbering on the load motor is somewhat arbitrary, but however
> these motors are connected, the poles are connected in parallel.
>
> Maybe you have a different definition of "connected in parallel". My
> definition is that potential between like points (L1 to L1, L2 to L2,
> L3 to L3) is zero. Current does flow from L3 of one motor to L3 of
> another.
>
> i
> (now I have more bells and whistles on my new phase converter, like
> balancing and power factor correction caps, dual idlers, blah blah,
> but they do not change the basic fact that these motors are indeed
> parallel connected)
>
>
> On Wed, 4 Jan 2006 13:20:04 -0600, Robert Swinney <jud...@comcast.net>
> --
>
jim rozen
>My RPC has no capacitors, starts and plug-reverses my lathe and mill
>just fine.
Wait. Don and Jim.... separated at birth?
:^)
Jim
jim rozen
>The only way the two 3-phase motors could be connected in parallel is if
>they are both fed from a 3-phase source.
Ah, this *is* a semantic minefield. I think I see your point finally.
They're not, and cannot be in parallel, if one thinks that being
in parallel means they each have that extra wire there. The
third leg doesn't, it's missing the extra external connection that
the line wire represents.
From a rough electrician's standpoint consider what the wiring
looks like when I have my drum switch turned on at the lathe, but
the converter is not energized at the knife switch on the wall.
L1 and L2 are missing. There's no external current source so
the third leg is now identical to all the others. At that point
then they truly are in parallel - from an electrican's view as
well as a EE's view.
When the converter is operating of course there is one special lead
that breaks the symmetry - it's missing the line connection. An
electrican would say that the absence of that line connection does
not change the fact the two sets of windings are in parallel. A
EE looks at the entire network as a system, including the incoming
power. He says parallel means all nodes have the same number of
connections.
Jim Stewart
> In article <34qdnaM8UfY...@comcast.com>, Robert Swinney says...
>
>
>>The only way the two 3-phase motors could be connected in parallel is if
>>they are both fed from a 3-phase source.
>
>
> Ah, this *is* a semantic minefield. I think I see your point finally.
>
> They're not, and cannot be in parallel, if one thinks that being
> in parallel means they each have that extra wire there. The
> third leg doesn't, it's missing the extra external connection that
> the line wire represents.
>
> From a rough electrician's standpoint consider what the wiring
> looks like when I have my drum switch turned on at the lathe, but
> the converter is not energized at the knife switch on the wall.
>
> L1 and L2 are missing. There's no external current source so
> the third leg is now identical to all the others. At that point
> then they truly are in parallel - from an electrican's view as
> well as a EE's view.
>
> When the converter is operating of course there is one special lead
> that breaks the symmetry - it's missing the line connection. An
> electrican would say that the absence of that line connection does
> not change the fact the two sets of windings are in parallel. A
> EE looks at the entire network as a system, including the incoming
> power. He says parallel means all nodes have the same number of
> connections.
I'm glad I have VFD's and don't have to
use so much brainpower figuring out how
they work (:
Robert Swinney
I can see. Hanrahan didn't show the load motor, only assigned terminal
numbers 1, 2 and 3 to it. I would have to assume he meant T1 and T2 on the
idler went to windings 1 and 2 of the motor. And it would be a fair guess
he intended for those same connections to go to windings 1 and 2 of the load
motor; granted those would be in parallel. But T3 on the idler, let's call
that an "outside" end of the winding for the sake of convention, goes to 3
on the load. Wouldn't it be a safe guess then that 3 on the load is an
outside end of that coil also? I believe the confusion comes from the fact
the 3rd leg is both source and load in a RPC instead of a single lead tied
back to a common source as in a true parallel arrangement. Hey! You almost
got it below, when you said, "because the third leg of the idler is a
driving leg rather than a driven leg." The third leg is both a driver and a
driven leg, plain and simple. The 3rd leg is a part of a complete network
(mesh it if you like) and it cannot be separated into a generator only
portion of the RPC. The RPC consists of an idler and a load with the 3rd
leg serving as both generator and consumer - not server only as if it were a
simple parallel connection.
See the explanation given to Iggy, copied here for your convenience:
""Now look at the way current flows in the L3 lead. The idler's L3 wire has
1
end connected to the 3rd. winding on the idler, call that a source point for
L3 current flow. The other end of wire L3 connects not to the analogous
same start point on the load motor but to a point on the other end of the
load motor's L3. This is not, can not, be considered a parallel connection.
The only way the two 3-phase motors could be connected in parallel is if
they are both fed from a 3-phase source.
In a manner of speaking, for a RPC (network) to do its thing, when taking in
*single-phase* current and delivering *3-phase current* to a load motor
(also part of the network) there has to be current flow in 2 directions in
the
3rd leg. Of course, aggregate current flow is such that current will flow
in the "right" direction in the load motor's 3rd leg. Parts of the RPC act
as both generators and consumers, thus the heavier element will cause
current to flow, seemingly backwards, into the other element. And so it is
with the RPC - capacitor augmentation can enhance the convoluted current
flow in such a way as to make emulated 3-phase current flow in the load
motor.""
As for wizardry and witchcraft, I see none in the operation of a RPC,
balanced or not. Try to embrace the idea of the 3rd leg as both generator
and consumer, and you'll have less trouble when you try to mesh things out.
I will leave the horrendous math up to you as you seem to have already
figured it out.
Bob Swinney
"Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
news:5haor19vukh9iusqe...@4ax.com...
> reversal in I-Z drop They are not essential to the
Robert Swinney
>
> Ah, this *is* a semantic minefield. ***I think I see your point
> finally.***
>
> They're not, and cannot be in parallel, if one thinks that being
> in parallel means they each have that extra wire there. The
> third leg doesn't, it's missing the extra external connection that
> the line wire represents.
>
> From a rough electrician's standpoint consider what the wiring
> looks like when I have my drum switch turned on at the lathe, but
> the converter is not energized at the knife switch on the wall.
>
> L1 and L2 are missing. There's no external current source so
> the third leg is now identical to all the others. At that point
> then they truly are in parallel - from an electrican's view as
> well as a EE's view.
>
> When the converter is operating of course there is one special lead
> that breaks the symmetry - it's missing the line connection. An
> electrican would say that the absence of that line connection does
> not change the fact the two sets of windings are in parallel. A
> EE looks at the entire network as a system, including the incoming
> power. He says parallel means all nodes have the same number of
> connections.
Jeeze, Jim! Thanks, I think. And just about when I pictured you with your
ball cap turned around the right way and it said "Gary Coffman" on the bill.
Bob Swinney
jim rozen
>Jeeze, Jim! Thanks, I think. And just about when I pictured you with your
>ball cap turned around the right way and it said "Gary Coffman" on the bill.
I always thought that gary's insights to matters like this (EE related)
were typically very valid. And he was the one who suggested that
flywheels probably hurt rather than help.
I think that gary would see your "not really parallel" view of life
and agree mostly.
But honestly, whenever I have to tell somebody how to "make" a phase
converter, they're typically electrically-savvy folks who want to
run a machine. The easiest way to explain it to them is to say
"you put the two idler motor leads across the line, and then you
put the load motor smack dab in parallel with the idler leads.
Basically there's a one-to-one correspondence between the leads
of the idler and the load motor. No wires left over and all that
sort of thing. Then they say "but what about the fact that the
idler has the two incoming line leads hung on it?" and then I
say "don't worry about those, the thing'll work just fine with
them there."
Red to red, black to black, blue to blue. Electricians like color
codes. This is why I drive them crazy when I wire my motorcycles
with all white wire. Makes drawing the diagram easy. "What color is
*this* wire?"
"White."
Don Foreman
wrote:
>
>When the converter is operating of course there is one special lead
>that breaks the symmetry - it's missing the line connection. An
>electrican would say that the absence of that line connection does
>not change the fact the two sets of windings are in parallel. A
>EE looks at the entire network as a system, including the incoming
>power. He says parallel means all nodes have the same number of
>connections.
>
>Jim
He does? In circuit analysis, a set of two-terminal networks are
regarded as "in parallel" if they are each connected to the same pair
of nodes so the voltage across them is identically the same.
Similarly, a set of n-terminal networks are in parallel if they are
connected to the same set of n nodes so the various inter-terminal
voltages on each n-terminal network are identically the same for
corresponding pairs of terminals. This is regardless of whatever
else might be connected to, between or among those nodes and
regardless of any external symmetry or lack thereof. Some nodes may
well have more connections than other.
By this definition, if there are wires connecting each terminal of
one device to a corresponding terminal of another device, they
are in parallel -- regardless of what else might be connected to those
terminals.
Don Foreman
<jud...@comcast.net> wrote:
>Well, you're reading a lot more into the Hanrahan drawing (conv/fig 1) than
>I can see. Hanrahan didn't show the load motor, only assigned terminal
>numbers 1, 2 and 3 to it. I would have to assume he meant T1 and T2 on the
>idler went to windings 1 and 2 of the motor. And it would be a fair guess
>he intended for those same connections to go to windings 1 and 2 of the load
>motor; granted those would be in parallel. But T3 on the idler, let's call
>that an "outside" end of the winding for the sake of convention, goes to 3
>on the load. Wouldn't it be a safe guess then that 3 on the load is an
>outside end of that coil also? I believe the confusion comes from the fact
>the 3rd leg is both source and load in a RPC instead of a single lead tied
>back to a common source as in a true parallel arrangement. Hey! You almost
>got it below, when you said, "because the third leg of the idler is a
>driving leg rather than a driven leg." The third leg is both a driver and a
>driven leg, plain and simple. The 3rd leg is a part of a complete network
>(mesh it if you like) and it cannot be separated into a generator only
>portion of the RPC. The RPC consists of an idler and a load with the 3rd
>leg serving as both generator and consumer - not server only as if it were a
>simple parallel connection.
The roles of "generator" and "server" just have to do with direction
of current flow, in a parallel connection or otherwise. For
example, the elements of a parallel-resonant circuit alternately act
as energy source and energy sink. Even though they have the same
voltage impressed across them, they may (usually do) have currents
flowing in opposite directions.
>
>See the explanation given to Iggy, copied here for your convenience:
>
>""Now look at the way current flows in the L3 lead. The idler's L3 wire has
>1
>end connected to the 3rd. winding on the idler, call that a source point for
>L3 current flow. The other end of wire L3 connects not to the analogous
>same start point on the load motor but to a point on the other end of the
>load motor's L3. This is not, can not, be considered a parallel connection.
Why not?
>The only way the two 3-phase motors could be connected in parallel is if
>they are both fed from a 3-phase source.
How they are (are aren't) fed by an external system does not change
the way they are connected! "Parallel connection" is a matter of
physical topology.
>
>In a manner of speaking, for a RPC (network) to do its thing, when taking in
>*single-phase* current and delivering *3-phase current* to a load motor
>(also part of the network) there has to be current flow in 2 directions in
>the
>3rd leg. Of course, aggregate current flow is such that current will flow
>in the "right" direction in the load motor's 3rd leg. Parts of the RPC act
>as both generators and consumers, thus the heavier element will cause
>current to flow, seemingly backwards, into the other element.
Yet it isn't a generator. Hmmm......
>And so it is with the RPC - capacitor augmentation can enhance the convoluted current
>flow in such a way as to make emulated 3-phase current flow in the load
>motor."
It's threephase with or without the capacitors, though the phases may
be unbalanced with different-than-ideal phase relationships and
magnitudes. The caps just improve balance under a given set of
conditions.
>
>As for wizardry and witchcraft, I see none in the operation of a RPC,
>balanced or not. Try to embrace the idea of the 3rd leg as both generator
>and consumer, and you'll have less trouble when you try to mesh things out.
>I will leave the horrendous math up to you as you seem to have already
>figured it out.
I think we each have things figured out, though clearly not in the
same way. There are lots of ways to look at things. The concept
of rotating fields is a fiction and an artifice, as is the practice
of dealing with complex impedances using the (imaginary) square root
of -1 as EE's are so fond of dong. There are lots of ways to
think about what's going on. They aren't necessarily mutually
exclusive.
Robert Swinney
parallel with each other because it connects from one end of one winding to
the *other* end of the other winding. Voltage symmetry and a parallel
connection as commonly defined cannot exist under those conditions. By your
definition below, the wire does not connect one terminal of one device to a
corresponding terminal of the other device. Granted, the 2 line terminals
do meet that criteria but the 3rd leg terminals do not. Thanx, Jim for
taking Don by the hand and trying to help him out. I think he is getting
there. At least he has come up with a plausible definition of "parallel".
That's progress!
Bob Swinney
"Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
news:d36pr11vg1eit5hob...@4ax.com...
Robert Swinney
"Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
>
>>
>>In a manner of speaking, for a RPC (network) to do its thing, when taking
>>in
>>*single-phase* current and delivering *3-phase current* to a load motor
>>(also part of the network) there has to be current flow in 2 directions in
>>the
>>3rd leg. Of course, aggregate current flow is such that current will flow
>>in the "right" direction in the load motor's 3rd leg. Parts of the RPC
>>act
>>as both generators and consumers, thus the heavier element will cause
>>current to flow, seemingly backwards, into the other element.
>
> Yet it isn't a generator. Hmmm......
>
>
>
>>And so it is with the RPC - capacitor augmentation can enhance the
>>convoluted current
>>flow in such a way as to make emulated 3-phase current flow in the load
>>motor."
>
> It's threephase with or without the capacitors, though the phases may
> be unbalanced with different-than-ideal phase relationships and
> magnitudes. The caps just improve balance under a given set of
> conditions.
No. A RPC is not a three-phase device in the classical sense; It isn't fed
with 3-phases and it does not "generate" 3 phases as would, say a 3-phase
alternator. True, the currents circulating in the load motor may make you
think they are 3-phase but that is because they are the products of a
special network. That network is *not* comprised of motors having all 3
sets of leads connected in parallel. Because of the way it is connected,
that network has the capability of taking single-phase current into two
3-phase motors and delivering currents that emulates true 3 phase current.
Key to accomplishing this is the non-parallel connection between the 3rd
legs.
Bob Swinney
dca...@krl.org
running on a single phase source, and then connect the three leads of
the motor to a three phase rectifier bridge. Do I not have three phase
power going to the rectifier bridge? Is my ripple current not pretty
much what I would expect if I had the rectifier bridge connected to the
output of a three phase generator? It seems to me that a RPC does not
need a load motor to work.
Dan
Don Foreman
wrote:
>In article <m20or19216tv9k3ei...@4ax.com>, Don Foreman says...
>
>>The rotor field is always in space quadrature from the stator field.
>>This is well-established in about any textbook on the subject. That
>>being the case, the emf it induces in the third leg is necessarily
>>in quadrature with the emf impressed by the line (and countered by the
>>stator field) in the other two windings.
>
>I thought it was the rotor *current* that was in quadrature.
It is. Same thing. Ampere's law. Field is proportional to current.
Don Foreman
<jud...@comcast.net> wrote:
>Sorry, Don. The lead between the 3rd leg terminals does not place them in
>parallel with each other because it connects from one end of one winding to
>the *other* end of the other winding.
Ah, the *other* end of a three-terminal network. I have so much to
learn!
>Voltage symmetry and a parallel
>connection as commonly defined cannot exist under those conditions. By your
>definition below, the wire does not connect one terminal of one device to a
>corresponding terminal of the other device. Granted, the 2 line terminals
>do meet that criteria but the 3rd leg terminals do not.
There's only three freakin' terminals, there ain't no *other* end.
Further, parallelism has no requirement of voltage symmetry.
Parallelism, in conventional terms, is a matter of topology.
Further, internodal voltages are what they are, however labelled,
symmetrical or not, whether or not they match your expectations.
Terminals connected together are nodes by definition -- in
conventional terminology. If the labelling doesn't match then the
labelling is wrong. The issue here may be "as commonly defined" as
that doesn't match your theory. Progress here: it's good to clarify
where your theory deviates from common definition and conventional
engineering terminology.
>Thanx, Jim for
>taking Don by the hand and trying to help him out. I think he is getting
>there. At least he has come up with a plausible definition of "parallel".
>That's progress!
Yes, thanks Jim! I particularly like the idea of using all white
wires.
jim rozen
>Yes, thanks Jim! I particularly like the idea of using all white
>wires.
Cuts down on a lot of confusion, it does. <g>
jim rozen
>>When the converter is operating of course there is one special lead
>>that breaks the symmetry - it's missing the line connection. An
>>electrican would say that the absence of that line connection does
>>not change the fact the two sets of windings are in parallel. A
>>EE looks at the entire network as a system, including the incoming
>>power. He says parallel means all nodes have the same number of
>>connections.
>He does? In circuit analysis, a set of two-terminal networks are
>regarded as "in parallel" if they are each connected to the same pair
>of nodes so the voltage across them is identically the same.
WEll yes. I didn't say it was a conventional definition. I think
electricians (and a good many other folks) will give a resounding
<huh?> when exposed to it. But it's *internally* consistent.
Robert Swinney
> running on a single phase source, and then connect the three leads of
> the motor to a three phase rectifier bridge. Do I not have three phase
> power going to the rectifier bridge? Is my ripple current not pretty
> much what I would expect if I had the rectifier bridge connected to the
> output of a three phase generator? It seems to me that a RPC does not
> need a load motor to work."
Yes, Dan (I think) you'd have 3-phase current going to the rectifier
bridge. This is true by virtue of the fact a 3-phase motor running on
single-phase delivers 3 phase currents to a resistive load. Notice, I did
not say "generates" 3-phase current because the original single-phase line
terminals are connected through to the resistive load and the other "phase",
if you will, is derived via transformer action within the 3-phase motor.
The 3rd. leg voltage, and current, into the rectifier will (obviously) be
less than the single-phase line voltage suplied directly to the rectifier.
Now, stop at this point and forget the rectifier. The description above
would apply equally well if the load on the idler was composed of 3 light
bulbs, also a resistive load. In that case, the light connected directly
across the single-phase line would burn at full brilliance while the other 2
bulbs connected from the 3rd leg to L1 and L2 respectively would burn at
less than full brilliance.
IMO, your other point re. a RPC needing a load motor to work is moot. This
because an idler motor alone is not a RPC.
Bob Swinney
<dca...@krl.org> wrote in message
news:1136439960.3...@g44g2000cwa.googlegroups.com...
Robert Swinney
bleats:
"You are right, it does not need a load motor. You could run a resistive
load (a 3 ph heater), or, like I do, a 3 phase welder that starts with a
transformer and rectifier."
Bob (does not suffer trolls) Swinney
Christopher Tidy
As Jim says, this does seem to be a semantic minefield. But I suspect
that were people face-to-face they could hammer out their differences
fairly quickly. It is often the way on Usenet.
My take on the contentious issues is as follows.
The idler motor will generate a voltage at the third terminal when not
connected to a load, but it cannot supply any generated power because no
current can be drawn. The difference here is between generated voltage
and generated power.
I would say that the RPC idler and load motors are in parallel in a
topological sense. However, the current flow within the windings of the
motors will be very different from what would be seen if the two motors
were connected in parallel across a three phase supply. I suspect that
this is the root of the disagreement here.
All are fair points.
Chris
Christopher Tidy
<snip>
> My RPC has no capacitors, starts and plug-reverses my lathe and mill
> just fine.
Out of interest, what are the horsepower ratings of your RPC idler and
lathe and mill main motors?
Chris
Christopher Tidy
> On Tue, 3 Jan 2006 21:07:42 +0000 (UTC), Christopher Tidy
> <cdt22...@cantabgold.net> wrote:
>
>
>
>>I can't seem to find any used flywheels to fit my motor, but I can get a
>>brand new flywheel for £40. I'm not sure if it is worth it in order to
>>satisfy my scientific curiousity. If I get a different motor, I can get
>>a flywheel for next to nothing, but that will involve lots of effort,
>>bartering and deals in order to get a motor which isn't quite so cool.
>>
>
>
> I won't touch the theoretical discussions on this thread. However I
> thought I might mention that if you wanted to experiment cheaply I'm
> sure you can find a used cast iron pulley in large enough diameter to
> serve as your flywheel. Preferably a multi-groove pulley.
Thanks for that thought, Wayne. It actually entered my head a month or
two ago, but for some reason I'd forgotten about it again. I have a
couple of two-groove cast iron pulleys which fit this motor. Each weighs
about 10 lb and is about 8" in diameter. I'm not sure if I can fit two
on the shaft, but it'll certainly take one.
It seems like there is no data regarding flywheels on RPC idlers. A few
people have suggested that it may help with plug reversing (which is
what I was thinking) but it seems unclear what the effect will be while
the convertor is running in a steady state. My motor already has a
pretty heavy rotor (about 8" diameter), but the energy stored will be
reduced by the fact that it spins fairly slowly (940 rpm). My aim is to
get the best performance out of a convertor with a limited idler size.
If I get chance to experiment with a flywheel and acquire some data, I
will. Thanks for all the input.
Chris
Jim Wilson
> The idler motor will generate a voltage at the third terminal when not
> connected to a load, but it cannot supply any generated power because no
> current can be drawn.
I don't understand how it's possible by the laws of physics for both of
these statements to be true.
Jim
Robert Swinney
"> I would say that the RPC idler and load motors are in parallel in a
> topological sense. However, the current flow within the windings of the
> motors will be very different from what would be seen if the two motors
> were connected in parallel across a three phase supply. I suspect that
> this is the root of the disagreement here."
Well, how's that for getting at the crux of the biscuit, eh? Semantics are
us! You display a depth of understanding that goes way past most of the
arguments set forth in this thread. Your description, above, very aptly
conveys a depth of appreciation for the manner in which currents must flow
in a RPC. Perhaps in trying to describe those currents, my use of the term
"convoluted" was an unwise choice. I suppose it was not "technically
precise" enough for some of the intelligencia on RCM for they sought to jump
on words and skip over any element of mutual comprehension. Apparently
there was no "mutual comprehension" save for maybe Jim Rozen and yourself.
Parallel was another bad choice of words - although it apparently had more
technical appeal to those that demand precise engineering definition. Many
of the respondents chose to pick on the absolute definition of "parallel"
while totally overlooking the context in which it was used.
Bob Swinney
Don Foreman
I think he refers to a case where the third leg of the idler has no
external connection; that terminal is just hangin' out in the breeze.
It could still exhibit a voltage, but no current flows because there
is no circuit in which it can flow. If no current flows thru that
terminal , then no power is transferred into or out of it.
Don Foreman
Idler is 5 HP. Lathe is 3 or 5 HP, mill is 1 HP. My idler runs
the lathe just fine when the lathe is set to the 3HP setting, but
can't quite hack it on the 5 HP setting. If I needed the higher
speeds (2x) of the 5 HP setting, I'd probably need a bit larger
idler.
It might pull it if it were a belt-drive lathe or had a clutch, but
it's a gearhead lathe. It tries to work on the 5 HP setting, but it
blows the breaker in the lathe before it can get wound up to speed.
Adding some capacitors probably would help some, but I think a bigger
idler would be the best solution. I'm content to use it as is. 1000
RPM is fast enough to do everything I want to do on that lathe.
The 1 HP mill has no problem operating at any speed. Smaller motor,
less inertia.
jim rozen
Ah, hang on there. The field in the rotor has to be 180 degrees
out from the stator fields, from Lenz's law, right?
Christopher Tidy
> Chris sez:
>
> "> I would say that the RPC idler and load motors are in parallel in a
>
>>topological sense. However, the current flow within the windings of the
>>motors will be very different from what would be seen if the two motors
>>were connected in parallel across a three phase supply. I suspect that
>>this is the root of the disagreement here."
>
>
> Well, how's that for getting at the crux of the biscuit, eh? Semantics are
> us! You display a depth of understanding that goes way past most of the
> arguments set forth in this thread.
Well, I had the benefit of reading all your posts before I wrote a
response! Thanks for the compliment.
I'm cleaning and painting the idler at the moment. Should be looking at
a first test run as soon as I've wound a new secondary to provide 240 V
-> 415 V conversion.
Best wishes,
Chris
Christopher Tidy
That's exactly what I meant.
Chris
Christopher Tidy
Thanks for those figures. All more data to add to the thought "melting pot".
Chris
Robert Swinney
"> In my opinion you need to realize that a RPC is an induction generator."
Dan, I know you have some experience with induction generators so I'll ask
you to respectfully consider that:
An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?
Bob Swinney
<dca...@krl.org> wrote in message
news:1136387823.4...@g49g2000cwa.googlegroups.com...
>
> Robert Swinney wrote:
>> IMO, you need to lose the thinking of a RPC as being a form of generator.
>>
>> Bob Swinney
>
>
>
> As far as flywheels are concerned, a flywheel will keep the slip angle
> from changing as quickly. So a RPC without a flywheel will draw power
> from the mains more quickly when the load is increased. Score points
> for that side. On the other hand, a RPC with a flywheel will draw
> power from the flywheel when the load is increased as well as from the
> mains. So score points for the other side.
>
> In the real world, it does not make much difference as the change in
> speed of the RPC should be slight, and therefore only a small amount of
> power can be drawn from the flywheel. Having a flywheel would help
> with an undersized RPC when the load motor is plugged.
>
>
> Dan
>
Don Foreman
wrote:
>In article <r5ipr11v62s97pjh6...@4ax.com>, Don Foreman says...
>>
>>On 4 Jan 2006 10:09:34 -0800, jim rozen <jim_m...@newsguy.com>
>>wrote:
>>
>>>In article <m20or19216tv9k3ei...@4ax.com>, Don Foreman says...
>>>
>>>>The rotor field is always in space quadrature from the stator field.
>>>>This is well-established in about any textbook on the subject. That
>>>>being the case, the emf it induces in the third leg is necessarily
>>>>in quadrature with the emf impressed by the line (and countered by the
>>>>stator field) in the other two windings.
>>>
>>>I thought it was the rotor *current* that was in quadrature.
>>
>>It is. Same thing. Ampere's law. Field is proportional to current.
>
>Ah, hang on there. The field in the rotor has to be 180 degrees
>out from the stator fields, from Lenz's law, right?
I was vague, sorry. I meant rotor current. Rotor field (the field
the rotor produces) is in phase with rotor current by Ampere's law
relating magnetic field to current.
That field is produced by rotor current resulting from EMF induced in
the rotor by rate of change of stator field linking it -- Lenz's law,
as you say. Rotor current is then this EMF / rotor_impedance.
The rate of change is at slip speed -- stator flux rotates at synch
speed, rotor rotates at slip rpm below synch speed. This is from
the perspective of an observer on the rotor, using the artifice of
rotating fields of constant magnitude to represent sinusoidally
varying fields in space quadrature. The equivalance is mathematically
correct, and a convenient way to look at things. It isn't the only
way to look at things by any means, but I find it easiest to
visualize. Reference: "Electric Machinery", Fitzgerald & Kingsley,
McGraw Hill.
Rotor field and stator field can be dealt with separately and
independently, as when resolving vectors into components. They differ
in phase because induced voltage in the rotor is the time derivative
of stator flux apparently rotating at slip speed. They are usually
very nearly in quadrature because the rotor impedance looks primarily
resistive to rotor emf induced at slip frequency. Slip frequency is
typically about 2.5 Hz at rated speed so rotor self-reactance is
negligable.
Robert Swinney
an induction generator. The induction generator (one made from a common
induction motor) will generate when excited by the mains and when its rotor
is driven by external means to a speed exceeding that of the motor's
synchronous speed. Slip is said to be negative under these conditions.
Bob Swinney
"Robert Swinney" <jud...@comcast.net> wrote in message
news:vdKdneZSYLD...@comcast.com...
Don Foreman
<jud...@comcast.net> wrote:
>Dan sez:
>"> In my opinion you need to realize that a RPC is an induction generator."
>
>Dan, I know you have some experience with induction generators so I'll ask
>you to respectfully consider that:
>
>An induction motor is a consumer, not a generator. As you know true
>induction generators (induction motors) have to be excited by overdrive from
>the AC mains in order to generate. Tht is not done in any fashion in a RPC.
>The RPC is a load on the mains, not a supplier to the mains. Again, I'll
>say, we need lose the idea of a RPC being a generator. Think of it as more
>of a converter; well, that's part of it's name now isn't it?
>
>Bob Swinney
A fella by the name of Swinney said elsewhere that idler and load
motor function both as generators and loads. True statement.
Emf is produced in all three windings of the idler. In the driven
windings, those connected to the mains, that emf is slightly less than
applied voltage so the current in those windings is (Vline -
Vemf)/Zwnding. A similar but phase-displaced emf is also produced
in the third leg. This emf can then drive (supply power to) the
third leg of the load motor which also is not connected to the mains.
So neither the idler nor the load are generators from the perspective
of the mains, but the idler, regardless of what else you may call it,
does supply current and power to the load motor's third leg.
I would therefore argue that the idler alone is a rotary phase
converter (RPC) because it produces a voltage on its third leg that
is of different phase from the mains voltage whether or not it has a
load connected to it. It isn't a rotary power converter (also RPC)
unless there is a load connected, because if there is no load
connection then the idler's third leg has no current so there is no
different-phase power.
In either case, this different phase is not exactly right in
magnitude or phase to make the result balanced threephase, though if
the idler is big enough (low impedance) it'll be pretty close. This
is because the IZ drops in the driven windings of the idler are
different in polarity wrt the emf than is the case in the third leg.
The discrepancy can be reduced with capacitors, at least for a
particular load motor and particular mechanical or useful load.
jim rozen
>I would therefore argue that the idler alone is a rotary phase
>converter (RPC) because it produces a voltage on its third leg that
>is of different phase from the mains voltage whether or not it has a
>load connected to it. It isn't a rotary power converter (also RPC)
>unless there is a load connected, because if there is no load
>connection then the idler's third leg has no current so there is no
>different-phase power.
But, but, but.
No tune capacitors.
No pf correction.
No potential relay or starting capacitors.
No contactors, no control transformers.
It can't *possibly* work. These things have to be complicated.
<http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg>
Pardon me, I have to go make some chips... <g>
jim rozen
>Rotor field and stator field can be dealt with separately and
>independently, as when resolving vectors into components. They differ
>in phase because induced voltage in the rotor is the time derivative
>of stator flux apparently rotating at slip speed. They are usually
>very nearly in quadrature because the rotor impedance looks primarily
>resistive to rotor emf induced at slip frequency. ...
OK, makes sense to me.
Robert Swinney
"> A fella by the name of Swinney said elsewhere that idler and load
> motor function both as generators and loads. True statement."
Yeah, But! That's not quite how I said it. I believe I said elements of a
RPC function as both generators and consumers because of the way current
flows in an entire RPC, not just in the idler motor.
Don, dig out the little paper I sent you a couple of years ago and in there
you will see some diagrams describing current flow in a RPC - an entire RPC;
You do still have that little paper, don't you? Naw! I suppose not or else
you wouldn't have slipped into the Iggy school of RPC's.
Bob Swinney
Robert Swinney
a saw but here goes:
When I said: ">>Sorry, Don. The lead between the 3rd leg terminals does
not place them in
>>parallel with each other because it connects from one end of one winding
>>to
>>the *other* end of the other winding. "
This concept was immediatly poo-pooed by the "if its connected as a RPC,
then it is in parallel". Later, then a definition of parallel was given as:
"By this definition, if there are wires connecting each terminal of one
device to a corresponding terminal of another device, they are in
parallel -- regardless of what else might be connected to those
terminals."
Consider 2 wye motors connected as a RPC, seemingly in parallel. It appears
to me that 2 wye motors connected in parallel by the definition of
corresponding terminals, above, are not in parallel by that definition
unless the "star" or neutral points within each motor are connected by a
solid lead. Then, all corresponding points are connected.
RPC connected motors do not meet the criteria.
Kapeesh?
Bob (getting tired of all this)Swinney
Don Foreman
<jud...@comcast.net> wrote:
>Don sez:
>
>"> A fella by the name of Swinney said elsewhere that idler and load
>> motor function both as generators and loads. True statement."
>
>Yeah, But! That's not quite how I said it. I believe I said elements of a
>RPC function as both generators and consumers because of the way current
>flows in an entire RPC, not just in the idler motor.
OK, but what does that mean? Currents in an entire anything flow
thru the elements that comprise it, so current flow(s) in an entire
RPC must flow thru its elements. The idler and the load motor are
elements, are they not? Do you mean RPC to connote rotary phase
converter? Do you assert that an RPC must have capacitors to be
called an RPC? Is it the capacitors that function as both generators
and loads?
>Don, dig out the little paper I sent you a couple of years ago and in there
>you will see some diagrams describing current flow in a RPC - an entire RPC;
>You do still have that little paper, don't you? Naw! I suppose not or else
>you wouldn't have slipped into the Iggy school of RPC's.
Naw, I suppose not. I recall it, but I don't seem to have it on
either computer. If it was paper, I certainly no longer have it.
I must say I respect Iggy's rather consistent practice of
courteous and civil discourse.
Don Foreman
<jud...@comcast.net> wrote:
>The key point here is: "How my phase converter is wired when it runs a load
>motor". The flawed logic is that a phase converter does not "run" a load
>motor. Such a differentiation between phase converter and load motor is not
>possible. An idler motor and load motor, taken together as a network, are
>what constitutes a rotary phase converter. This all harks back to the
>misunderstood "generator" concept as applied to an idler motor. The two
>must work together to form a rotary phase converter. Remember a RPC (the
>whole RPC) acts to manipulate current flow in a network so that the load
>motor voltages, and currents, are the same as if the load motor was
>operating from a 3-phase source. Remembering, all the while, the whole thing
>is running on *single-phase* current.
>
>Now as for parallel connectivity: The drawing is that of a classic RPC
>(idler and load motor) operating from Hot 1 and Hot 2, both sides of a
>single-phase source. Consider Hot 1. It connects to L1 of the idler motor
>and also to L1 of the load motor. The same can be said for Hot 2 and the 2
>respective L2's. By definition, the points designated as L1 and L2 in both
>idler and load are operated in parallel across the line. That is to say the
>2 main windings, L1 to L2 in your drawing of both idler and load are
>connected in parallel across the line.
>
>Now look at the way current flows in the L3 lead. The idler's L3 wire has 1
>end connected to the 3rd. winding on the idler, call that a source point for
>L3 current flow. The other end of wire L3 connects not to the analogous
>same start point on the load motor but to a point on the other end of the
>load motor's L3.
What "other end"? Nobody rewound the motor. It connects to the same
terminal that motor came with.
>This is not, can not, be considered a parallel connection.
>The only way the two 3-phase motors could be connected in parallel is if
>they are both fed from a 3-phase source.
They are connected in parallel regardless of how they are fed. The
locus of confusion may be this: if you consider a Y connection, the
third legs are in series with each other, though the three-terminal
networks (idler and load motor) are connected in parallel. The
function of an RPC is to make the voltage on L3 resemble the voltage
of a third mains line in phase and magnitude if one were present.
>
>In a manner of speaking, for a RPC (network) to do its thing, when taking in
>*single-phase* current and delivering *3-phase current* to a load motor
>(also part of the network) there has to be current flow in 2 directions the
>3rd leg.
There's current flow in both directions everywhere in an AC system.
If you meant to say power flow, I disagree. Power flows from idler
third leg to load motor third leg. Net power over each cycle in
L3 is, by definition for RPC function, flowing into the load same
as it is on the other two lines just as would be the case if an actual
third mains line of different phase were feeding L3 and the load
motor. There will be some reactive component and power factor in
all three legs, but they won't be greatly different from each other
in an RPC that is working well.
I agree that the RPC must be treated as a system to get the voltage
on L3 to be right, because that voltage is determined by the idler,
the load motor and any capacitances that are present.
Another confusion factor is that the system is driven by "single"
phase. How d'ya get three phases with one more wire? The trick to
undestanding this is to regard the 220 mains as 110v and 110v<180
(180 out of phase with the first line) either side of a neutral
which may or may not actually exist as it does in the US and Canada.
That can be viewed as being produced by two vectors of 127 volt
magnitude with phase difference of 120 degrees. Let's take a snapshot
in time where these vectors are at 120 and 240 degrees. The
resulting line-to-line voltage is 220, though the unconnected
neutral is now non-zero and in quadrature with the actual mains
voltages, a voltage vector at 0 degrees in our snapshot. The third
leg in the idler, referred to neutral in in a Y- connected motor,
produces additional quadrature voltage, at 0 degress in our snapshot,
as described in another post. If the magnitude and phase of the
idler's third-leg contribution is just right, the resulting voltages
on L1, L2 and L3 will look like balanced threephase mains.
The contribution of the third leg will never be "just right", hence
the addition of capacitors to adjust phase and magnitude as they
resonate with the various inductive reactances in the system.
> Of course, aggregate current flow is such that current will flow
>in the "right" direction in the load motor's 3rd leg.
What is aggregate current flow? Average current flow in any AC
circuit is zero.
> Parts of the RPC act as both generators and consumers,
Which parts?
> thus the heavier element will cause
>current to flow, seemingly backwards, into the other element. And so it is
>with the RPC - capacitor augmentation can enhance the convoluted current
>flow
What does "convoluted current flow" mean? Convoluted compared to
what? Even if the earnest reader deduces that the context is
"intricate, complex, labyrinthine" rather than "rolled in a coil",
it doesn't add a bit to his understanding of how an RPC works.
Guys of our age, training and experience should be teaching what we
know, Bob. I'd like to see a higher standard of contribution from
you than I might expect from some others. I I think you know a
lot but I think you could do a lot better job of teaching. Being
tall enough to skip derision of readers who respectfully (or
otherwise) disagree or "don't yet get it" wouldn't hurt a bit.
>in such a way as to make emulated 3-phase current flow in the load
>motor.
>
>Bob Swinney
I think you have the general ideas right, but I really doubt that
someone who didn't already have some understanding of how these things
work would be helped by your explanation. Further, it's not right
and not at all contributive to deride others who don't comprehend
what you meant rather than what you said.
>
>
>
>"Ignoramus18299" <ignoram...@NOSPAM.18299.invalid> wrote in message
>news:BDVuf.25892$f26....@fe75.usenetserver.com...
>> Here's how my phase converter is wired when it runs a load motor:
>>
>>
>> idler Load
>>
>> L3-------------------------L3
>> / \ / \
>> L1 --- L2 L1---L2
>> | | | |
>> | +--------------------->---+
>> +-----------------------------+ Hot2
>> Hot1
>>
>> L1 connected to L1, L2 connected to L2, L3 connected to L3. L1 and L2
>> are also connected to utility power Hot1 and Hot2.
>>
>> How are these motors not running in parallel?
>>
>> They are.
>>
>> Leg numbering on the load motor is somewhat arbitrary, but however
>> these motors are connected, the poles are connected in parallel.
>>
>> Maybe you have a different definition of "connected in parallel". My
>> definition is that potential between like points (L1 to L1, L2 to L2,
>> L3 to L3) is zero. Current does flow from L3 of one motor to L3 of
>> another.
>>
>> i
>> (now I have more bells and whistles on my new phase converter, like
>> balancing and power factor correction caps, dual idlers, blah blah,
>> but they do not change the basic fact that these motors are indeed
>> parallel connected)
>>
>>
>> On Wed, 4 Jan 2006 13:20:04 -0600, Robert Swinney <jud...@comcast.net>
>> wrote:
>>> Well, Don - you've missed the point again! What part of "2 induction
>>> motors operating from single phase current in a RPC configuration cannot
>>> be
>>> in parallel" did you fail to understand. Your well intentioned, and
>>> colorful, drawings were not of a RPC configuration. Draw out a RPC and I
>>> think you may understand. Oh! be sure to include some capacitors. They
>>> (in
>>> electronic terms) might be considered as steering capacitors, for it is
>>> their job to force the convoluted currents to flow in such a way as to
>>> *emulate* true 3-phase. Note, I said *emulate* because current flow in a
>>> RPC is not the same as current flow in parallel connected 3-phase motors,
>>> no
>>> matter which transform is used.
>>>
>>> Bob Swinney
>>> "Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
>>> news:mr4or15vae0bt47e3...@4ax.com...
>>>> On Wed, 4 Jan 2006 11:45:55 -0600, "Robert Swinney"
>>>> <jud...@comcast.net> wrote:
>>>>
>>>>>Don,
>>>>>
>>>>>See my previous post, where I tried to show 2 induction motors operating
>>>>>from single phase current in a RPC configuration cannot be in parallel.
>>>>>
>>>> I saw it. I just don't agree with it. See recent post showing things
>>>> in 3D.
>>>>
>>>> Transform to Y using the usual Y-delta transforms if you like. See
>>>> any textbook on the subject.
>>>>
>>>> In the Y case they don't look in parallel if there is no neutral
>>>> connection. However, since a delta depiction clearly shows that they
>>>> *ARE* in parallel, they are in freakin' parallel, BOB! Must I glue
>>>> up some popsicle sticks for you?
>>>>
>>>> Can you explain the discrepancy? :<)
>>>>
>>>> Hint: if there is no potential between unconnected points (the
>>>> neutrals in a Y configuration) then they are effectively connected.
>>>>
>>>> Don "half-cocked" Foreman
>>>> half cocked my arse....grumble mutter ....chuckle
>>>>
>>>>
>>>
>>>
>>
>>
>> --
>>
>
Don Foreman
<ignoram...@NOSPAM.20351.invalid> wrote:
>On Sat, 07 Jan 2006 00:21:44 -0600, Don Foreman <dfor...@NOSPAMgoldengate.net> wrote:
>>
>> I must say I respect Iggy's rather consistent practice of
>> courteous and civil discourse.
>>
>
>Thank you Don. If I barge into some interesting discussion with
>insults, am I really going to learn more?
>
>i
That's up to you. I've learned some good stuff from some
insufferably arrogant assholes. Please don't read that as an implied
shot at Bob. Bob and I have corresponded for years. He ain't a bad
guy most days.
Hm, I wonder if there might be some others who have regarded me as an
insufferably arrogant asshole along the way. Oh well, fuck 'em
if they can't take a joke. :<)
It's not hard to ignore the skeeterbites if there are good fish to be
caught.
Don Foreman
Poo-pooed? That connotes fluffy dismissal. I flat disagreed.
I do capish. Kapeesh indeed! Texas is obviously a long ways from
Brooklyn, Ol' Son. Roger thet, big ol' ten-four. Yer waltz ain't
quite in synch with mah foxtrot, but we ain't that fur apawrt.
See recent post. They're still topologically connected in parallel
per conventional definition, but I can see how one might regard them
as functionally in series, particuarly if neutral floats as it must
in an RPC.
In any case, my chainsaws are put away for the MN winter and I'm way
too lazy to pull a Swedesaw anymore.
>
>Bob (getting tired of all this)Swinney
What, time for your nap? (ducking.....)
Robert Swinney
see your name in print. Maybe, I am wrong.
Bob Swinney
"Ignoramus20351" <ignoram...@NOSPAM.20351.invalid> wrote in message
news:CtJvf.29835$lK2....@fe80.usenetserver.com...
> On Sat, 07 Jan 2006 00:21:44 -0600, Don Foreman
> <dfor...@NOSPAMgoldengate.net> wrote:
>>
>> I must say I respect Iggy's rather consistent practice of
>> courteous and civil discourse.
>>
>
Robert Swinney
withstanding. Take another look at your line below where you say, "but I
> as functionally in series, particuarly if neutral floats as it must
> contention that the idler and load of a RPC are not truly connected in
> parallel unless there is a solid connection between the 2 respective
> neutral points. That satisfies the definiton of corresponding points being
> connected, doesn't it?? Can we call your special definition of parallel
> as applied to RPC's, maybe, huh, "quasi parallel"?
Bear with me for one more moment, please (courteously).
We have a 3-phase source and wish to connect n numbers of 3-phase loads
across it, in parallel. You'd have to agree there would be a "phase"
connected to each of the 3 input terminals (nodes ?) of the loads. In other
words, the connections looking into the loads would be in parallel, and
connected across the 3-phase source, would they not? OK, if you're with me
(I'm a poor teacher, I know), now disconnect the 3-phase source and look at
the loads, say, call one of them an idler and the rest of them loads. Now
the idler and load are not truly in parallel, by definition, because the
lead between star points (neutrals) is not there.
Now consider, a RPC (rotary phase converter) connected as in what I call
"quasi parallel" for want of a better description. You might agree, the
idler and load are not in true parallel because the solid lead between
neutrals is missing.
But they are connected as a RPC must be. Current from L1 to L2 "sees" the
RPC as a series load. Current flow via the 3rd leg and the 2 line legs into
the load, as connected in RPC fashion, results in circulating currents
throughout that appear to the load as 3 phases. (emulation?) As you've
said elsewhere, a RPC would not be possible if the neutrals were connected
as in what I deem to be a true parallel connection. Therefore, it seems
that in a RPC, the idler and load are not truly connected in parallel.
Bob Swinney
"Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
news:2ctur111812ng7vfd...@4ax.com...
Robert Swinney
trying to explain my understanding of the RPC, I offer the following.
Generators and consumers: Motor windings, (elements of a RPC for example)
consume energy and give it up as torque. Those same windings also generate
energy in the form of counter EMF. In essense current is flowing in 2
directions through the winding. In electronic parlance, you might say there
is both a voltage rise and a voltage fall. I have sense and education
enough to know average current flow in an AC circuit is zero, but you have
tap danced all around the point, by even mentioning it. (Patronizingly,
perhaps)
Aggregate current: That which flows in a network as a result of everything
going on in the network.
Convoluted current: In a manner of speaking, that current which flows in
the load side of a RPC.
BTW much of the definition you question was duly addressed in the little
paper I sent you awhile back. At the time your comments were to the effect
the paper was well researched, well written, etc.
Bob Swinney
pent...@yahoo.com
<dfor...@NOSPAMgoldengate.net> wrote:
>On Tue, 3 Jan 2006 23:14:07 -0600, "Don Young" <no...@nonesuch.com>
>wrote:
>
>>Since the running idler and load motors are directly connected in parallel,
>>wouldn't plug reversing with identical motors and no mechanical load have an
>>equal chance of reversing either motor? When running free, it seems to me
>>that either motor could be considered to be the source or load for the third
>>phase leg. I tend to believe that the idler requires more mechanical inertia
>>than the load to maintain the best functioning.
>
>Interesting! The relative impedances are also important here. The
>larger motor with lower impedance (and probably higher inertia) will
>govern. Look at the terminal voltage where the two third legs are
>connected. If the motors were perfectly matched, their effects would
>cancel and this terminal voltage would be zero. If they are not
>matched, the voltage (phase) of that terminal will be determined by
>the motor with the lower impedance, and the phase of this voltage
>determines (or indicates) the direction in which both motors turn.
>>
>>If an induction motor does not "generate", is induced counter EMF imaginary
>>and the use of common induction motors as generators impossible? There are
>>many ways to understand and describe how things work and I like to think of
>>the RPC as simply a running induction motor with the magnetized rotor
>>inducing EMF not only into the line energized windings (counter EMF) but
>>also into the unenergized and phase displaced windings.
>
>Right, up to here.
>
>> Note that, when
>>disconnected and still turning, an induction motor still has voltage across
>>its windings and loading this voltage with "braking" resistors will
>>mechanically load the rotor.
>
>Only if the rotor has some significant permanent magnetism -- not
>usually the case.
A squirrel cage motor DOES generate a back EMF and will continue
to do so for several revolutions after all power has been removed
even if it has zero permanent magnetism.
In the case of a 2 pole motor, at the instant of disconection,
the induced circulating currents in the short circuited rotor
inductance provide a diametrical NS field which decays at at the
rotor L/R rate for several tenths of a second. The voltage
generated by this decaying field is is easily observed with an
oscilloscope - the initial voltage is close to full supply
voltage.
Jim
Don Foreman
<jud...@comcast.net> wrote:
>Don, now you are beginning to get the idea, my poor teaching technique not
>withstanding. Take another look at your line below where you say, "but I
>can see how one might regard them
>> as functionally in series, particuarly if neutral floats as it must
>> in an RPC." Yes, neutral *must* float in a RPC but it is still my
>> contention that the idler and load of a RPC are not truly connected in
>> parallel unless there is a solid connection between the 2 respective
>> neutral points. That satisfies the definiton of corresponding points being
>> connected, doesn't it?? Can we call your special definition of parallel
>> as applied to RPC's, maybe, huh, "quasi parallel"?
>
>Bear with me for one more moment, please (courteously).
>
>We have a 3-phase source and wish to connect n numbers of 3-phase loads
>across it, in parallel. You'd have to agree there would be a "phase"
>connected to each of the 3 input terminals (nodes ?) of the loads. In other
>words, the connections looking into the loads would be in parallel, and
>connected across the 3-phase source, would they not? OK, if you're with me
>(I'm a poor teacher, I know), now disconnect the 3-phase source and look at
>the loads, say, call one of them an idler and the rest of them loads. Now
>the idler and load are not truly in parallel, by definition, because the
>lead between star points (neutrals) is not there.
It has finally occurred to me that the neutral is what's causing the
confusion.
Nearly all three phase machines are three-terminal devices. There
may be a physical neutral in a Y-connected machine, but it's rarely
used. We agree that the neutrals would not be connected with
Y-connected idlers and loads. If they were delta-connected, there'd
be no neutrals to connect.
Consider a delta-connected idler and load(s). There are wires
connecting each terminal of the idler to corresponding terminals on
each load. The machines are connected in parallel. Each winding of
the idler is in parallel with a corresponding winding in the load(s).
There are only three nodes in this circuit. Now connect mains
to two of the three terminals. We haven't broken any connections,
so the idler and load(s) are still connected in parallel, each
winding in the idler is still in parallel with a corresponding winding
in the load(s). There are still only three nodes in the circuit,
with power fed to two of them. The power line is connected across
one winding and one phase. We might not know what the potentials
across the other two phases might be, but it's clear that the
voltages across corresponding phases of the two machines are the
same. They're in parallel.
Now consider Y-connected idler and load(s). The winding not tied to
mains on the idler is in series with the corresponding winding on the
load. There are still 3 nodes, the two that mains are connected
to and the one between the two third windings.
Are these machines still in parallel? I assert that they are.
The confusion comes from looking at those windings that are connected
in series and referring to neutral.
In a Y-connected machine, a winding is not a phase. A phase is from
terminal to terminal whether the windings within are delta or Y
connected.
Each phase in a Y connected machine has two series-connected windings
from one terminal to the other. Each winding is a member of two
adjacent phases, and each phase has two windings in series. If you
draw a circle around each *phase* (not winding) of a Y-connected
machine, from terminal to terminal, you see that the idler phases are
indeed connected in parallel with the load phases, whether or not
there are any power lines connected. Let's leave the power off for a
moment. You see not just one, but three loops of four windings in
series -- two idler windings and two load windings. But each phase
in the idler is still in parallel with it's corresponding phase in
the load.
Now connect real threephase power to the terminals. I think you've
agreed that in this situation the idler and load are still in
parallel. Phase currents are currents into a terminal, and are the
same as line currents when the system is driven with threephase
power. Each winding has two phase currents flowing thru it, so the
net current in any winding is the vector sum of these two currents.
Now remove the threephase feed and connect a single phase power line
to two terminals, or one phase, and try to figure out what's going on
in the other two phases with the terminal between those two phases (on
both idler and load) connected to nothing else. We see two
windings in series between neutral of idler and neutral of load. But
the same situation is true with the other windings! You can go from
neutral to neutral via three routes, each thru one winding in the
idler and a corresponding winding in the load. If you drew circles
around the *phases* (pairs of windings) before, you'll see that each
phase in the idler is still connected in parallel with a corresponding
phase in the load.
It's tempting to think of a phase as line to neutral thru just one
winding, because that looks easier to understand. But it's
incorrect unless the neutrals are actually connected because the
voltages from the third node to the other two nodes, the other two
phase voltages, do not depend only on the windings connected to the
third node. Similarly, the current thru the wire connecting the third
nodes does not depend solely on the voltage from third nodes to their
respective neutrals unless those neutrals are tied together or
otherwise held at some known potential from one neutral to the other.
Don Foreman
<jud...@comcast.net> wrote:
>Don, in as much as you've railed against some of the definitions I used in
>trying to explain my understanding of the RPC, I offer the following.
>
>Generators and consumers: Motor windings, (elements of a RPC for example)
>consume energy and give it up as torque. Those same windings also generate
>energy in the form of counter EMF. In essense current is flowing in 2
>directions through the winding.
So my ammeter needs two needles?
> In electronic parlance, you might say there
>is both a voltage rise and a voltage fall.
Whoa! My voltmeter needs two needles too?
Just kidding, Bob. I know what you mean: sometimes its easier to
think of voltages and currents as vector sums of component voltages
and currents,
> I have sense and education
>enough to know average current flow in an AC circuit is zero, but you have
>tap danced all around the point, by even mentioning it. (Patronizingly,
>perhaps)
I know you do. In the following sentence I suggested that perhaps
you meant power flow which made sense in context.
>
>Aggregate current: That which flows in a network as a result of everything
>going on in the network.
Well, in that context the aggregate current in a balanced threephase
system is zero though the currents in various branches are certainly
non-zero.
>
>Convoluted current: In a manner of speaking, that current which flows in
>the load side of a RPC.
>
>BTW much of the definition you question was duly addressed in the little
>paper I sent you awhile back. At the time your comments were to the effect
>the paper was well researched, well written, etc.
I didn't recall the definitions, but I do recall the comment and I
wouldn't have said it if I didn't mean it. That must have been two
computers ago because I can't find your writeup in this machine or
the last one.
Don Foreman
>A squirrel cage motor DOES generate a back EMF and will continue
>to do so for several revolutions after all power has been removed
>even if it has zero permanent magnetism.
>
>In the case of a 2 pole motor, at the instant of disconection,
>the induced circulating currents in the short circuited rotor
>inductance provide a diametrical NS field which decays at at the
>rotor L/R rate for several tenths of a second. The voltage
>generated by this decaying field is is easily observed with an
>oscilloscope - the initial voltage is close to full supply
>voltage.
>
> Jim
I stand corrected. It makes sense, now that you point it out. L/R
ratio is pretty high because R is quite small.
Thanks, Jim!
Don Foreman
<dfor...@NOSPAMgoldengate.net> wrote:
> Each winding has two phase currents flowing thru it, so the
>net current in any winding is the vector sum of these two currents.
True for delta connection, not for Y. In a Y each phase voltage is
the vector sum of two winding voltages.
pent...@yahoo.com
<dfor...@NOSPAMgoldengate.net> wrote:
>On 4 Jan 2006 13:22:13 -0800, jim rozen <jim_m...@newsguy.com>
>wrote:
>
>
>>
>>When the converter is operating of course there is one special lead
>>that breaks the symmetry - it's missing the line connection. An
>>electrican would say that the absence of that line connection does
>>not change the fact the two sets of windings are in parallel. A
>>EE looks at the entire network as a system, including the incoming
>>power. He says parallel means all nodes have the same number of
>>connections.
>>
>>Jim
>
>He does? In circuit analysis, a set of two-terminal networks are
>regarded as "in parallel" if they are each connected to the same pair
>of nodes so the voltage across them is identically the same.
>Similarly, a set of n-terminal networks are in parallel if they are
>connected to the same set of n nodes so the various inter-terminal
>voltages on each n-terminal network are identically the same for
>corresponding pairs of terminals. This is regardless of whatever
>else might be connected to, between or among those nodes and
>regardless of any external symmetry or lack thereof. Some nodes may
>well have more connections than other.
>
>By this definition, if there are wires connecting each terminal of
>one device to a corresponding terminal of another device, they
>are in parallel -- regardless of what else might be connected to those
>terminals.
Just to stir things up a bit further I register my support for
BOTH the parallel and non parallel camps - it just depends on how
you look at the circuit operation.
If we regard the idler plus load motors as two connected
passive three terminal networks the there can be no doubt that
this is a straightforward parallell connection. No playing with
words on the way any further conections are made (e.g single
phase power input) can alter this.
However,when the motors have rotating rotors, BOTH motors
accept input power on two of their terminals and BOTH try to
deliver output power to the third linked phantom phase
connection.
The direction of the power flow through the phantom phase
link then depends on the relative mechanical loading on the two
rotors. In the two limiting conditions of both motors idling or
both motors loaded to the same fraction of their rated HP, each
motor is self sufficient and little or no third phase power flows
through the link. In the normal case of one idling and one
loaded, the power flow is from idler to load motor.
It is equally valid to regard this current as a circulating
current within a parallel connected system or as the current
developed in the series connection of an idler generator to its
load motor
Jim
Don Foreman
> The direction of the power flow through the phantom phase
>link then depends on the relative mechanical loading on the two
>rotors. In the two limiting conditions of both motors idling or
>both motors loaded to the same fraction of their rated HP, each
>motor is self sufficient and little or no third phase power flows
>through the link. In the normal case of one idling and one
>loaded, the power flow is from idler to load motor.
>
> It is equally valid to regard this current as a circulating
>current within a parallel connected system or as the current
>developed in the series connection of an idler generator to its
>load motor
See my later post that addresses this issue of series vs parallel.
The situation is quite clear if idler and load are delta-connected:
there is no neutral and phases are clearly in parallel however they
may or may not be connected to singlephase or 3phase mains.
You know of and about Delta - Y transformations of three-terminal
networks, particularly symmetrical threephase machines.
Everyone seems to agree that any neutrals that might exist in an RPC
system are not connected. If neutrals are not connected or
don't exist, then I say they can and should be ignored. Absent
neutrals, the question of phase-to-phase and device-to-device
parallelism seem quite clear to me.